Question

If `vec F` is the force acting in a particle having position vector `vec r` and `vec tau` be the torque of this force about the origin, then
A. `r. tau = 0 and F. tau=0`
B. `r xx tau = 0 and F xx tau ne 0`
C. `r. tau ne 0 and F. tau ne 0`
D. `r xx tau ne 0 and F xx tau =0`

Answer 1

Correct Answer - A
Torque, `tau = r xx F` i.e., `tau` is perpendicular to both r and F
`:. tau.r=0 and tau.F=0`